Abstract
Echinochloa spp. is one of the most invasive weeds in rice fields worldwide. Acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibiting herbicides are two of the most widely used rice herbicides. However, overuse has led to the resistance evolution of Echinochloa spp. to penoxsulam (ALS-inhibitor) and cyhalofop-methyl (ACCase-inhibitor). In this work, 137 different Echinochloa spp. populations were collected in different rice fields in Extremadura (western Spain) where lack of control was detected. Target-site based resistance (by sequencing ALS and ACCase gene) and characterization of Echinochloa species at the molecular level (based on PCR-RFLP analyses) were carried out in those populations. Most of the populations studied (111 of 137) belong to the E. oryzicola/E. oryzoides group. Three-point mutations were identified in ALS genes: Pro197Ser, Pro197Thr, and Ser653Asn, the first being the most frequent substitution in resistant plants. In the ACCase gene, the Ile1781Leu substitution was found. In both ALS and ACCase sequencing, evidence of heterozygosity was also observed. To assess whether cross-resistance patterns differed between mutations, two populations belonging to the E. oryzicola/E. oryzoides group had its most frequent mutations (Pro197Ser, population ech3-14 and Ile1781Leu, population ech114-10) chosen to be carried out in a dose-response assay. It was confirmed that Pro197Ser conferred resistance to triazolopyrimidine, imidazolinone, sulfonylurea, and pyrimidinyl benzoate families. On the other hand, the Ile1781Leu change gave resistance to aryloxyphenoxypropionate and cyclohexanedione families. Of the authorized herbicides in rice in Spain, more that 80% belong to these families. It is therefore important that farmers carry out an integrated control system that combines both chemical and non-chemical tools.
Highlights
Spain is one of the main rice producers in Europe, with an estimated 107,604 ha dedicated to rice cultivation in the 2017 season [1]
Seeds of 137 Echinochloa spp. populations were collected from 4 different rice areas in Extremadura, in fields where lack of control by commonly used herbicides was reported by farmers (Figure 1)
The results of molecular characterization using Polymerase Chain Reaction (PCR)-RFLP showed 111 populations belonging to the E. oryzicola/E. oryzoides group, 20 populations to the E. crus-galli/E. hispidula group, and 6 populations to the E. colona
Summary
Spain is one of the main rice producers in Europe, with an estimated 107,604 ha dedicated to rice cultivation in the 2017 season [1]. Weeds are considered the worst pest affecting the rice production in Europe [2]. Echinochloa spp. are the most economically important weeds affecting rice, causing severe yield reductions [3]. Barnyard grass (E. cruss-galli (L.) Beauv.) is the most common weed species and is found in a wide range of summer crops such as rice. Late watergrass (E. oryzicola Vasing.) and early watergrass (E. oryzoides (Ard.) Fritsch.) are considered to be serious weeds of water-seeded rice in many rice production areas [4,5]
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